urea cycle

1. Urea Cycle
Dr Megha Bhise

2. Urea cycle/Kreb’s – Hanseleit
cycle/Ornithine – Urea cycle
• Introduction
• Site
• Enzymes
• Steps
• Regulation
• Significance
• Metabolic defect in urea cycle

3. Introduction
• Urea is the end product of protein
metabolism, it synthesized in liver and
excreted through kidneys
• Nitrogen of amino acid converted to ammonia
which is toxic to body
• Ammonia converted to urea
Site - Liver

4. Enzymes
• Carbamoyl phosphate synthetase – I (CPS-I)
• Ornithine transcarbamoylase (OTC)
• Arginosuccinate synthetase
• Arginosuccinate lyase
• Arginase

5. Steps of Urea Cycle

6. Over all reaction
NH4 + CO2 + Aspartate + 3 ATP
Urea + Fumarate + 2 ADP + 2Pi + AMP
+ PPi

7. Regulation
 Carbamoyl phosphate synthetase – I ( rate
limiting step)
N- acetylglutamate
Protein rich diet

8. • Significance of urea cycle
 Detoxication of ammonia into non-toxic
urea
 Regulation of blood pH

9. Metabolic defect in urea cycle
Disorder Enzyme defect Product accumulated
Hyperammonemia type -I Carbamoyl phosphate
synthetase – I
Ammonia
Hyperammonemia type -II Ornithine
transcarbamoylase (OTC)
Ammonia
Citrullinemia Arginosuccinate synthetase Citrulline
Arginosuccinic aciduria Arginosuccinate lyase Arginosuccinate
Arginemia arginase Arginine

10. THANK YOU !!!